fix: only write metrics if there is a useragent

internal/server/tail.go

@@ -39,6 +39,7 @@ func parseFunc(t *tail.Tail) {
 			continue
 		}
 
+		if len(l.Request.Headers.UserAgent) != 0 {
 			metrics.GetOrCreateCounter(
 				fmt.Sprintf(
 					`%s_http_request_total{host="%s", proto="%s", method="%s", status="%d", user_agent="%s"}`,
@@ -61,5 +62,8 @@ func parseFunc(t *tail.Tail) {
 					l.Status,
 				),
 			).Update(l.Duration)
+		} else {
+			slog.Warn("got empty user agent", "headers", l.Request.Headers)
+		}
 	}
 }